The present invention relates to a propeller shaft transmission structure for a tractor comprising an engine mounted forwardly of a driver's section and at a forward position of a main frame, a transmission case mounted rearwardly of the driver's section and at a rearward position of the main frame, and a propeller shaft interconnecting an engine output shaft extending rearwardly from the engine and a transmission input shaft extending forwardly from the transmission.
In a known transmission structure of the type noted above, the engine output shaft and the transmission input shaft are disposed at the same level, and the two shafts are interconnected by a propeller shaft extending horizontally, as disclosed in Japanese Utility Model Publication Kokai No. 61-110428. The tractor having such a transmission structure has a deck of the driver's section upwardly bulging along an intermediate position between right and left steps, and the propeller shaft extends through a housing defined by the bulging deck portion.
When driving the tractor having the above construction, the driver must place his feet across the bulging deck portion. The driver is thus compelled to take an uncomfortable driving posture.
With a view to allowing the driver to take a more comfortable driving posture, a proposal has been made to secure an increased foot space. In the proposed construction, as illustrated in FIG. 4, the transmission case is modified to dispose the input shaft at a lower level, and the propeller shaft 6 extends rearwardly and downwardly, whereby the the bulging deck portion between the steps is reduced in height.
According to the proposed construction, however, the transmission input shaft 9 is located at a much lower position than the engine output shaft 5, which results in an increased joint angle .alpha.. This construction thus has the disadvantages of low transmission efficiency, increased noise and rapid wear.